Setting the Church Thermostat

If a building, such as a church, is used only a few hours a week, in most cases it makes economic sense to turn the heat down when the building is not in use.

Ask Mr. Tight-Watt

Our readers have enquiring minds. And when it comes to energy efficiency, Mr. Tight-Watt and his cadre of experts can provide answers to these questions. This month, we have asked John Steil, Midwestern Energy Solutions, Oelwein, Iowa, to answer a question posed to Mr. Tight-Watt.

Question: The church I go to has a boiler heating system. Some say that the heat should not be turned down when the church is not being used because it costs more to get the temperature back up than it does to keep the heat up 24/7 even though the church is only used a few hours a week. What is your recommendation? –Joyce N., a Smart Choices reader

John’s Answer: This is a good question, probably one that many building owners struggle with. There are many variables that might affect the answer, including efficiency of the boiler, indoor temperature set point, outdoor temperature, cubic volume of air in the church and of course, how much air infiltration into the building exists.

In her question, Joyce states that the church is only used a few hours a week – indicating the church only needs to be brought up to a comfortable temperature during those few hours. I assume that no administrative people are in the church during hours when the congregation is not gathered for services. If it is a large church, then the volume of air to be conditioned is also large.

As it gets colder outside and the difference between indoor and outdoor temperatures (Delta-T) increases, the BTU required to condition the inside air will also increase. If the indoor temperature is trying to hold constant – say 68 degrees – then the thermostat is constantly indicating to the boiler system to obtain that set point. If on the days that the church is not being used and there is a larger Delta-T, then the boiler system is burning fuel in an attempt to keep the conditioned air at a thermostat set point (68 degrees). If there is no one inside the building, does it really need to be conditioned to the set point? Most likely not.

On the other hand, if the thermostat is turned down during times when the church is not being used, the boiler system will need less BTU (less fuel) to keep the church at the preset temperature. And if the thermostat temperature is increased, say an hour, before the congregation gathers, then the thermostat will call for an increase in temperature. The boiler system will come on and it will run for what seems like a long period of time to bring the indoor temperature up to the thermostat setting.

Bottom line: Most likely (depending on the condition of the building), the boiler system will not use as much fuel during that short period as it would if it were running at a constant temperature throughout the days while no one is in the church.

Your question comes at a very convenient time. Two weeks ago I performed a building performance test on an older church in a local community that also has a boiler system. We discovered that the building structure, walls and such were not leaking much air into the building. But we did find the bell tower was a huge issue for air leakage. The bell tower accounted for approximately 75% of the building’s total energy losses. Because of this, we recommended air sealing measures to correct the energy losses.

Do you have a question for Mr. Tight-Watt about lighting, insulation, heating and cooling, energy audits, ENERGY STAR, or other energy-efficiency questions? If so, send him your questions, and he'll respond in a future Smart Choices e-newsletter.